1. Field of the Invention
This invention relates to cooling tower and other direct contact heat and mass transfer devices fill assemblies and particularly to an improved splash-type fill bar construction for use in cooling tower installations.
Splash-type cooling towers utilizing "splash" fill media are well known in the art and have been widely used in the industry. They are generally characterized by streams of water falling on fill bars arranged in a geometrical pattern within a cavity beneath a water distributing system. The water falling by means of gravity splashes upon contact with the fill bars to form smaller droplets in a moving air stream.
In general, such cooling towers include a large housing through the side of which air is admitted and from the top of which the air is exhausted by suitable means such as exhaust fans. The water to be cooled is distributed throughout the housing from the upper surface of the housing by means such as the distributing pan. The water falls by gravity to a basin at the lower portion of the housing and is cooled during its descent by its intimate contact with air moving through the housing. During its descent, the water is broken into smaller droplets by splashing upon fill bars which are interspersed throughout the cavity defined by the interior of the housing. The splash fill bars thus break up the downward flow of water and provide surface area for commingling the water and air passing through the housing to promote cooling. As is well known, such cooling towers may be of the cross-flow type in which the air flows transversely to the descent of the water or of the counter-flow type in which the air travels in the direction opposite to the descent of the water. The improved splash bar and splash fill assembly of a cooling tower in accordance with the present invention is applicable to both counter-flow and cross-flow towers and is, in general, applicable to all types of towers in which the water is to be cooled or in which water provides the cooling medium.
More particularly, cooling towers employing splash-type fill may be characterized by the fact that streams of water fall upon fill bars arranged in a geometrical pattern wherein the water splashes upon contact and forms smaller droplets in a moving air stream. As the drops fall downwardly, some of the drops coalesce and impinge on lower splash bars, repeating the cycle. Exposure of the relatively warm drops of water to the moving air stream causes the water to cool and partially evaporate. Interrupting the fall of the individual drops by splashing on the fill bars, or sub-dividing into new drops to expose more surface area, promotes rapid cooling.
2. Description of the Prior Art
Splash-type fill bars have long been utilized in the art as an effective fill material for heat exchanging cooling towers. The earliest "splash" fill media, still in use today, merely consisted of rectangular or triangular wood slats, preferably made from redwood, upon which the water droplets cascading down from the top of the fill would hit the horizontal surface of the slats and "splash" or, in other words, divide into smaller droplets exposing a much larger surface for heat and mass transfer purposes.
The present splash bars are more commonly made from solid, extruded plastic material, sheet metal, aluminum or the like. These materials avoid the disadvantages of wooden splash bars, such as deterioration by rotting and increased possibility of fire hazard.
With the development of new synthetic materials, the cross-sectional configurations of splash fill bars used today vary considerably from application to application. Plastics, however, are not as rigid as wood and the major problem to be addressed in designing a plastic fill bar is the maximum distance it can span between adjacent supports. Four examples of splash bars having different configurations are disclosed in De Flon, U.S. Pat. No. 3,389,895 (the "V" bar); Furlong, U.S. Pat. No. 3,468,521 (the "Wedge" bar); Fordyce, U.S. Pat. No. 3,647,191 (the "M" bar); and Ovard, U.S. Pat. No. 4,133,851 (the "T" bar). All of these designs consist of relatively wide extruded plastic profiles that are perforated to conserve material and improve performance.
Indeed, it was determined very early that wide splash bars have a tendency to concentrate the water collected in heavy curtains of water instead of discrete droplets, and perforating the splash bars (with round or diamond-shaped holes) minimized this problem. This perforating operation, however, is costly and is usually made by a punching operation. As a result of perforating the splash bars, it is difficult to avoid the formation of micro-cracks at the edge of the holes. These cracks have a tendency to propagate, and ultimately small pieces of plastic will fall off and the slats will break. A major problem arises when these plastic fragments reach the heat exchangers or condensers and obstruct the heat exchanger or condenser tubes.
Another problem arises at the contact points between the plastic splash bars and their supporting wires. The vibrations due to impinging water and wind are enough to break the slats or bars at these points. The typical solution presently employed to combat this problem is the addition of "clips" to prevent direct contact of the wires to the slats. The addition of these "clips", however, is expensive and the labor needed to install them is extensive.
Fill assemblies comprising splash bars of a particular profile are chosen in accordance with the job requirements. Of course, all configurations should promote optimal cooling and uniformity of liquid disbursement. It should also be noted that manufacturers of splash bar fill material strive to obtain improved cooling performance and structural strength using less material. As an example of problems associated with various configurations, wide slats have been shown to accumulate a thick film of water on the upper surface which reduces the splashing effect of the large droplets. As a result thereof, the kinetic energy in the large droplets is partially expended by displacing the film of water already present on the upper surface. In this situation, only the remaining part of the slats, without the film of water, is used to generate small droplets. The result of a wide slat is fewer small droplets and consequently less heat transfer surface.
In addition, some of the prior art splash bars had an upper surface which was flat permitting liquid to accumulate thereon. Such a flat surface had a tendency to retain more water by capillarity. In such circumstances, the drainage of the liquid from the flat upper surface was severely limited by this configuration.
Some of the prior art splash bars also had edges of the upper surfaces which were rounded or at an obtuse angle from the adjacent side surfaces. If these edges are rounded or at an obtuse angle, the capillary forces have a tendency to prevent the formation of small droplets, and consequently, less heat transfer surface is utilized.